The present invention is directed to a technique for isolating a vehicle body carrier from an electrically charged vehicle body, and to vehicle body carriers employing such an electrical isolation technique. More particularly, the present invention is directed to a technique for isolating a vehicle body carrier from an electrically charged vehicle body, such that electrodeposition coating materials will not be attracted to and adhere to the vehicle body carrier.
Electrodeposition coating is well known in automotive and other vehicle manufacturing industries and, therefore, need not be described in detail herein. Basically, however, an electrically charged material (e-coat material) is coated to a vehicle body by imparting the vehicle body with a DC electrical charge that is opposite to that of a DC electrical charge imparted to the e-coat material. Consequently, when the vehicle and e-coat material are placed into contact (or near contact, in some cases), the e-coat material is attracted to and deposits on the oppositely-charged vehicle body. Such e-coat materials are generally applied to a vehicle body prior to primers (if used) and paints (often referred to as “white body” stage) to provide the vehicle body with improved corrosion resistance.
As considered in the present invention, electrodeposition coating is typically accomplished by immersing an unfinished vehicle body in a bath (tank) containing the e-coat material. With the vehicle body immersed in the tank of e-coat material, electric current is passed through both the vehicle body and e-coat material as described above. The e-coat material in contact with the vehicle adheres to the vehicle surface, building up an electrically insulating e-coat material layer over all areas of the vehicle body. Electrodeposition coating of a vehicle body is typically followed by passing the vehicle body through, for example, a rinsing operation and an oven.
In a vehicle manufacturing environment, the electrodeposition coating process typically occurs with the vehicle body attached to an assembly line conveyor vehicle body carrier. Therefore, both the vehicle body and vehicle body carrier are immersed in the e-coat tank during the electrodeposition coating process.
Subjecting the vehicle body carrier to an e-coat bath is generally problematic, however. That is, as described above, successfully coating an e-coat material to a vehicle body requires that the vehicle body be electrically charged. Because the carrier on which the vehicle body is supported during the electrodeposition coating process is moving, commonly on an overhead conveyor system, the required electrical charge is generally provided to the vehicle body from a bus, etc., associated with the overhead conveyor system. As the vehicle body and vehicle body carrier are commonly in conductive contact, the vehicle body carrier is also electrically charged, and of the same polarity as the vehicle body. This means, of course, that the vehicle body carrier will attract e-coat material in the same manner as the vehicle body while immersed in the e-coat bath.
This is an undesirable side effect of the electrodeposition coating process because long-term buildup of e-coat material on a vehicle body carrier may cause various problems. For example, such vehicle body carriers normally include various structures and components designed to interact with and to secure a vehicle body to the carrier. Excessive buildup of e-coat material on these structures and components can interfere with proper engagement between a vehicle body carrier and a vehicle body. The long-term buildup of e-coat material on a vehicle body carrier can also add significant weight to the vehicle body carrier, thereby imparting increased stresses on associated carrier support structures, drive systems, etc. Obviously, a buildup of e-coat material on a vehicle body carrier is also wasteful, as such material is intended for deposition only on an associated vehicle body, and the e-coat material cannot be reused once electrodeposited even if removed.
Consequently, based on the foregoing discussion, it can be understood that it would be desirable to prevent or at least greatly reduce the amount of e-coat material that adheres to a vehicle body carrier during the electrodeposition coating process. The technique and a resulting vehicle body carrier of the present invention allows for such a result.